In a liquid crystal display, for example, it is indispensable to dispose polarizers on both sides of a glass substrate providing a surface of a liquid crystal panel according to an image formation scheme adopted in the display. A polarizer is generally obtained in a procedure in which a polyvinyl alcohol-based film is dyed with a dichroic material such as iodine, thereafter, the film is crosslinked with a crosslinking agent and then, mono-axially stretched to thereby form a film. Since the polarizer is fabricated by stretching, it is easy to shrink. Since a polyvinyl alcohol-based film comprises a hydrophilic polymer, the film is very easily deformed especially in a humidified condition. Since the film itself is weak in mechanical strength, there has been a problem that the film is torn. Hence, adopted is a reinforced polarizing plate fabricated in a procedure in which a transparent protective film or transparent protective films each made from triacetyl cellulose or the like are adhered to on one side or both sides of a polarizer. The polarizing plate is fabricated by adhere the transparent protective film onto a polarizer using an adhesive.
A liquid crystal display in recent years has broadened applications, which covers a wide range from a portable terminal to a home large-sized TV, and sets of specifications have been provided for various kinds of applications. Especially, in the application of a portable terminal, a user as a precondition carries on while moving; therefore, the portable terminal has very severe requirements for durability. Therefore, a polarizing plate is required a durability that any of characteristics, and a shape does not change even in a humidified condition where dew drops are formed.
A polarizer is, as described above, used as a polarizing plate obtained by being reinforced with the transparent protective film. As adhesives for the polarizing plate conventionally used in adhesion of the transparent protective film to the polarizer, preferable is an aqueous adhesive, for example a polyvinyl alcohol-based adhesive prepared by mixing a crosslinking agent into a polyvinyl alcohol aqueous solution. A polyvinyl alcohol-based resin adhesive has had a case where the transparent protective film is peeled at the interface between the polarizer and the transparent protective film in a humidified condition. This is considered because the polyvinyl alcohol-based resin, which is a main component of the adhesive, is a water-soluble polymer and therefore, there occurs a possibility that the adhesive dissolves thereof in an environment of dewing.
In light of the problems, proposal has been made of an adhesive for polarizing plate comprising a polyvinyl alcohol-based resin having an acetoacetyl group and a crosslinking agent (for example, Patent Document 1). Even the adhesive for polarizer described in patent document 1, however, is insufficient in water resistance.                Patent Document 1: JP-A No. 7-198945.        